As American Girl only offers specific options in hair color, eye color, and skin tones (even within the Create Your Own Line), customization is the most popular way to have more unique dolls into a collection.
American Girl currently only offers three modifications to dolls outside of the Create Your Own line:
Dolls can also be modified to display limb loss through the company A Step Ahead Prosthetics at no cost; however, the company policy is to only offer customized dolls to children who have faced or are facing limb loss in order to aid in the strengthening of their foundation and self-confidence during their early developmental years and this is unavailable to the general public.
Some common types of unofficial modification are:
Unofficial modifications, especially extreme ones, are likely to result in a doll being unable to be repaired by the American Girl Hospital.